Communication scheme for channel quality information

ABSTRACT

A transmitter reports channel quality information by partitioning channel quality values, based on a channel quality information reporting parameter, into at least two partitions corresponding to different frequency bands in a bandwidth associated with the communications system. A channel quality value of the channel quality values of at least one of the at least two partitions is encoded to obtain signaling information on channel quality, including at least one of first channel quality information and second channel quality information, based on the channel quality information reporting parameter, wherein the second channel quality information is different from the first channel quality information. The transmitter transmits the signaling information on the channel quality by reporting the first channel quality information or the second channel quality information at different reporting frequencies depending on the channel quality information reporting parameter.

FIELD OF THE INVENTION

The invention relates to a method for receiving and a method forreconstructing channel quality information in a communication system.Further, the invention also provides a transmitter and receiverperforming these methods, respectively.

TECHNICAL BACKGROUND

Packet-Scheduling and Shared Channel Transmission

In wireless communication systems employing packet-scheduling, at leastpart of the air-interface resources are assigned dynamically todifferent users (mobile stations—MS). Those dynamically allocatedresources are typically mapped to at least one shared data channel(SDCH). A shared data channel may for example have one of the followingconfigurations:

-   -   One or multiple codes in a CDMA (Code Division Multiple Access)        system are dynamically shared between multiple MS.    -   One or multiple subcarriers (subbands) in an OFDMA (Orthogonal        Frequency Division Multiple Access) system are dynamically        shared between multiple MS.    -   Combinations of the above in an OFCDMA (Orthogonal Frequency        Code Division Multiplex Access) or a MC-CDMA (Multi Carrier-Code        Division Multiple Access) system are dynamically shared between        multiple MS.

FIG. 1 shows a resource-scheduling system on a communication channel forsystems with e.g., a single shared data channel. A transmission timeinterval (TTI) reflects the smallest interval at which the scheduler(e.g., the Physical Layer or MAC Layer Scheduler) performs the dynamicresource allocation (DRA). In FIG. 1, a TTI equal to one subframe (alsoreferred to as a time slot) is assumed. It should be noted thatgenerally a TTI may also span over multiple subframes.

Further, the smallest unit of radio resources (also referred to as aresource block), that can be allocated in OFDMA systems, is typicallydefined by one TTI in the time domain and by one subcarrier/subband inthe frequency domain. Similarly, in a CDMA system this smallest unit ofradio resources is defined by a TTI in the time domain and a code in thecode domain.

In OFCDMA or MC-CDMA systems, this smallest unit is defined by one TTIin time domain, by one subcarrier/subband in the frequency domain andone code in the code domain. Note that dynamic resource allocation maybe performed in the time domain and in the code/frequency domain.

The main benefits of packet-scheduling are the multi-user diversity gainby time domain scheduling (TDS) and dynamic user rate adaptation (DRA).

Assuming that the channel conditions of the users change over time dueto fast (and slow) fading, at a given time instant the scheduler canassign available resources (codes in case of CDMA, subcarriers/subbandsin case of OFDMA) to users having good channel conditions in time domainscheduling.

Specifics of DRA and Shared Channel Transmission in OFDMA

Additionally to exploiting multi-user diversity in time domain by TimeDomain Scheduling (TDS), in OFDMA multi-user diversity can also beexploited in frequency domain by Frequency Domain Scheduling (FDS). Thisis because the OFDM signal is constructed out of multiple narrowbandsubcarriers (typically grouped into subbands) in frequency domain, whichcan be assigned dynamically to different users. By this, the frequencyselective channel properties due to multi-path propagation can beexploited to schedule users on frequencies (subcarriers/subbands) onwhich they have a good channel quality (multi-user diversity infrequency domain).

In an OFDMA system the bandwidth is divided into multiple subbands forpractical reasons that consist out of multiple subcarriers. I.e., thesmallest unit on which a user may be allocated would have a bandwidth ofone subband and a duration of one subframe (which may correspond to oneor multiple OFDM symbols), which is denoted as a resource block (RB).Typically a subband consists of consecutive subcarriers. However in somecases it is desired to form a subband out of distributed non-consecutivesubcarriers. A scheduler may also allocate a user over multipleconsecutive or non-consecutive subbands and/or subframes.

For the 3GPP Long Term Evolution (see 3GPP TR 25.814: “Physical LayerAspects for Evolved UTRA”, Release 7, v. 7.0.0, June 2006—available athttp://www.3gpp.org and incorporated herein by reference), a 10 MHzsystem may consist of 600 subcarriers with a subcarrier spacing of 15kHz. The 600 subcarriers may then be grouped into 24 subbands (eachcontaining 25 subcarriers), each subband occupying a bandwidth of 375kHz. Assuming that a subframe has a duration of 0.5 ms, a resource block(RB) would span over 375 kHz and 0.5 ms according to this example.

In order to exploit multi-user diversity and to achieve scheduling gainin frequency domain, the data for a given user should be allocated onresource blocks on which the user has a good channel condition.Typically, those resource blocks are located close to each other and,therefore, this transmission mode is also denoted as localized mode(LM). FIG. 2 shows an exemplary data transmission to users in an OFDMAsystem in localized mode (LM) having a distributed mapping of Layer1/Layer 2 control signalling.

Alternatively, the users may be allocated in a distributed mode (DM). Inthis configuration a user (mobile station) is allocated on multipleresource blocks, which are distributed over a range of resource blocks.In distributed mode a number of different implementation options arepossible. For exemplary purposes a data transmission to users in anOFDMA system in distributed mode (DM) having a distributed mapping ofLayer 1/Layer 2 control signalling is shown in FIG. 3.

Link Adaptation

In mobile communication systems link adaptation is a typical measure toexploit the benefits resulting from dynamic resource allocation. Onelink adaptation technique is AMC (Adaptive Modulation and Coding). Here,the data-rate per data block or per scheduled user is adapteddynamically to the instantaneous channel quality of the respectiveallocated resource by dynamically changing the modulation and codingscheme (MCS) in response to the channel conditions. This may require atransmitter to have or obtain a channel quality estimate for the link tothe respective receiver. Typically hybrid ARQ (HARQ) techniques areemployed in addition. In some configurations it may also make sense touse fast/slow power control.

Channel Quality Information (CQI) Transmission

In a multi-user centrally managed system, a scheduler assignstransmission resources to several users as has been outlined above.Since generally the channel conditions for different users will varyover at least time and frequency, some sort of channel state or channelquality information is required at the scheduler, preferably transmittedfrom each user equipment device to the scheduler entity.

For most multi-user scheduler algorithms (except Round Robin), the mostaccurate channel state information should be for the strongest resourceblocks, to optimally assign a resource to a user where the channelexhibits a good quality. This will further be used in case that fortransmission of data, the modulation or coding scheme is adapted to thechannel quality, to increase the spectral efficiency, i.e., in caseswhere link adaptation is performed.

Generally the CQI is transmitted from a transmitting entity to areceiver entity. In the context of 3G radio network as in UMTS, where aNodeB may act as the multi-user management entity, as well as amulti-cell management entity, the CQI for the downlink transmissionchain is obtained (estimated) by a user equipment (UE), whichsubsequently transmits CQI to a NodeB. Therefore with respect to CQItransmission the user equipment acts as the transmitter entity, and theNodeB as the receiver entity.

Full Feedback

In case a full feedback is transmitted, i.e., the CQI information is notcompressed prior to transmission, a CQI value for each of the N_(rb)resource blocks is transmitted, giving the highest accuracy ofinformation at a very high cost of required transmission bits. To get arough estimate of the overhead on the CQI feedback information, a systembased on the following configurations may be considered: thecommunication system is equipped with 2×2 MIMO (Multiple Input MultipleOutput) using PARC (Per Antenna Rate Control), 20 MHz transmissionbandwidth (48 Resource Blocks), 0.5 ms CQI feedback interval, 1/3 rateturbo encoding, no-repetitions or puncturing, and with 24 bit CRCattached. The total CQI feedback overhead of this configuration would be2.904 Mbps per user.

CQI Compression

One approach to reduce the overhead induced by CQI signalling has beensuggested in 3GPP RAN WG#1 Tdoc. R1-061777, “DCT based CQI reportingscheme”, available at http://www.3gpp.org and incorporated herein byreference. The document proposes a scheme using a Discrete CosineTransform (DCT) to concentrate information into a small number ofcoefficients and discusses different mechanisms which coefficients, totransmit.

Strongest-M DCT and First-M DCT

The “Strongest-M” DCT scheme transmits the DC component of thetransformation and in addition M−1 most significant DCT coefficients.Assuming that M is known to transmitter and receiver, only indices ofthe transmitted coefficients as well as the values of the transmittedcoefficients need to be signalled. If M is not known by either thetransmitter or the receiver, the value of M may have to be signalled aswell.

The “First-M” DCT scheme transmits the M coefficients with the M lowestindex values. Assuming that M is known to transmitter and receiver, onlythe values of the transmitted coefficients need to be signalled. If M isnot known by either the transmitter or the receiver, the value of M mayhave to be signalled as well.

An example of a channel snapshot and an exemplary reconstruction of thechannel power using “Strongest 5” DCT scheme is shown in FIG. 8. Thecorresponding DCT of the complete (“Full DCT”) and compressed(“Strongest 5” DCT) channel information is shown in FIG. 9. While thechannel state may be reconstructed perfectly if all DCT coefficients(“Full DCT”) are transmitted, the channel state reconstruction willgenerally be suboptimum if only a subset of the DCT coefficients istransmitted. The choice of which DCT coefficients are transmitted willaffect the accuracy of the reconstructed channel state.

In the “Strongest 5” DCT scheme, only the 5 components with the largestmagnitude are chosen in the compression scheme. Since the DC componentmay be of increased importance, and as it can usually be expected to beamong the strongest components anyway, it may be preferable to alwaystransmit the DC coefficient. A bitmap that shows which 5 of the 24 DCTcomponents have the largest magnitude is given in FIG. 10, where a “1”value that the DCT component of that particular index belongs to one ofthe M largest magnitude coefficients.

It is a matter of convention whether the DCT components are labeled(numbered) from 0 to N_(rb)−1 or from 1 to N_(rb), or similar. Eitherway usually the DCT component with the lowest index is commonly referredto as the “DC coefficient” or “DC component” (DC=Direct Current).Without loss of generality a numbering ranging from 1 to N_(rb) isassumed in the examples described herein.

While the above mentioned approaches for transmitting the CQIinformation are based on performing a DCT on the channel stateinformation and encoding the resulting coefficients, there also existother schemes where the channel state information, i.e., the individualpower levels per resource block are encoded without performing atransformation.

3GPP RAN WG#1 Tdoc. R1-061819, “Overhead reduction of UL CQI signallingfor E-UTRA DL”, available at http://www.3gpp.org and incorporated hereinby reference, discusses a “Best-M” scheme for feedback reduction ofchannel quality signalling where a UE reports a label which indicatesthe M resource blocks with highest signal quality and additionally asingle channel quality indicator for these resource blocks. Assumingthat M is known to the transmitter and the receiver, signalling of the Mselected indices and the selected M values is needed in a CQI report.

A further scheme referred to as “Best M Individual” scheme reports thepower for each of the M best resource blocks, and average power forother resource blocks. Assuming that M is known to the transmitter andthe receiver, signalling of the M selected indices, the selected Mvalues, and the average value is needed in a CQI report. An exemplarybitmap that signals the best 5 out of 24 resource blocks is shown inFIG. 13.

A further scheme referred to as “Best M Average” reports the averagepower for M best resource blocks, and average power for other resourceblocks. Assuming that M is known to the transmitter and the receiver,signalling of the M selected indices and the two average values isneeded in a CQI report. An exemplary bitmap that signals the best 5 outof 24 resource blocks is shown in FIG. 13.

An example of a channel snapshot and an exemplary reconstruction of thechannel power using a “Best 5 Individual” scheme and a “Best 5 Average”scheme are shown in FIG. 11 and in FIG. 12, respectively. As can beseen, the “Best 5 Individual” scheme manages to give exact informationfor the 5 strongest resource blocks (number 8, 9, 10, 18, 19), but quitesubstantial deviations from the correct value for all other resourceblocks. The “Best 5 Average” scheme gives by chance quite accurateinformation for resource blocks 18 and 19, while we can identify largerdeviations—both better and worse—from the correct value for resourceblocks 8, 9, and 10. Likewise, for all other resource blocks thereconstructed value may exhibit large differences from the correctvalues.

Average CQI

Another scheme to reduce the CQI values is to determine the average CQIvalue and transmit this average value. This may be interpreted as aspecial case of a Best M=N_(rb) Average or Best M=0 Average scheme. Itrequires the least amount of transmitted information, however it alsooffers a generally very low accuracy with respect to the reconstructedresource block-wise channel quality information.

Signalling

Obviously, there is a need for using information symbols to convey theCQI from the transmitter to the receiver. Without loss of generality, itmay be assumed that bits can be used as information symbols. Using thenotations defined in subsequent sections, the number of bits requiredfor such signalling is illustrated in Table 1.

TABLE 1 Number of CQI Scheme required bits Full Feedback D · Nrb AverageD Best M Individual${D \cdot \left( {M + 1} \right)} + \left\lceil {{ld}\begin{pmatrix}N_{rb} \\M\end{pmatrix}} \right\rceil$ Best M Average${2 \cdot D} + \left\lceil {{ld}\begin{pmatrix}N_{rb} \\M\end{pmatrix}} \right\rceil$ DCT Greatest M (assuming that DCcoefficient is always transmitted)${D \cdot M} + \left\lceil {{ld}\begin{pmatrix}{N_{rb} - 1} \\{M - 1}\end{pmatrix}} \right\rceil$

As can be calculated from Table 1 and has been indicated above, the fullfeedback scheme requires a very high amount of bits to signal the CQI.This requirement may be too high to fulfill in a transmission system,particularly in cellular mobile radio systems where a large number ofentities have to report CQI values.

Also DCT-based schemes do not offer an optimal solution for transmittingthe CQI information. Since only a limited number of coefficients istransmitted in a DCT compression scheme, the reconstruction at thereceiver (which typically offers scheduling functions) is generally notoptimum for any resource block. Consequently there will be deviationsfor the strongest resource blocks, which will result in erroneousscheduler decisions or suboptimum adaptive modulation and codingdecisions by the link adaptation entity. Consequently the spectralefficiency is reduced.

In the “Best M Individual” scheme, very detailed information on thechannel state is transmitted for the strongest M resource blocks. Forall other resource blocks, the information available at the scheduler isextremely rudimentary.

Particularly in case that M is rather small, a problem occurs if a useris assigned more resource blocks than M resource blocks. In this case,some allocated resources are only allocated according to an averageresource block quality, which certainly is suboptimum. Furthermore, asubsequent link adaptation would also be based on such an average value,resulting in suboptimum link adaptation and consequently in reducedspectral efficiency. This problem may be circumvented by a high numberM, however at the drawback that a lot of feedback signalling is requiredin this case. Therefore another potential problem is to suggest a codingscheme that requires a small amount of feedback signalling.

In the “Best M Average” scheme, the problems are two-fold. On the onehand, a small number of M will result in similar problems as a small Min the “Best M Individual” scheme. Additionally, the accuracy of thebest M resource blocks reported is not as high as in the “Best MIndividual” scheme, further deteriorating the accuracy of scheduling orlink adaptation performance.

On the other hand, a simple increase of M is not guaranteed to improvethe behavior of the “Best M Average” scheme. Even though the number ofresource blocks which are contained within the signalled set increases,the averaging over those M resources will decrease the accuracy forthose resource blocks. Therefore there is an optimum M for which thenumber and level of detail provide the most accurate allocation or linkadaptation.

In any case, finding this value of M may not be trivial in a mobile orcellular environment, and—in addition—even when having found anappropriate M value, the achievable data transmission throughput in datatransmission is generally bad because of the averaging feature of thisscheme.

It should be obvious to those skilled in the art that the informationconveyed by the average CQI scheme is of very low accuracy. In order toperform meaningful resource scheduling or link adaptation usingCQI-dependant modulation or coding schemes, a higher accuracy than thatprovided by the average scheme has to be available.

SUMMARY OF THE INVENTION

One object of the invention is to suggest a scheme for transmittingchannel quality measures from a transmitter to a receiver that maymitigate at least one of the problems outlined above.

Another object of the invention is to suggest a scheme for communicatingchannel quality measures that on the one hand allows for an accuratereconstruction of the channel quality measures at the receiver and onthe other hand requires an acceptable transmission overhead.

At least one of these objects is solved by the subject matter of theindependent claims. Advantageous embodiments of the invention aresubject matters of the dependent claims.

According to one aspect of the invention, channel quality feedbackmeasures for a channel (e.g., per resource unit of the channel) aredivided into distinct partitions. Each partition consists only of asubset of the channel quality feedback measures. The partitioning of thechannel quality feedback measures may allow for reducing the amount ofoverhead that needs to be attributed to the signalling of channelquality information, as (in some embodiments) the partitioning may beadvantageously used to further reduce the amount of signallinginformation. Further, the partitioning may allow for a more accuratereconstruction of the channel state at the receiver, from whichscheduling and link adaptation may benefit.

Another aspect of the invention relates to the receiver that “inverts”the encoding (compression) scheme to reconstruct the channel qualitymeasures. In some exemplary embodiments of the invention, a schedulermay utilize the information on the channel condition to schedule airinterface resources of transmitters that are served by the scheduler.Moreover, alternatively or in addition thereto, the reconstructedchannel estimate may also be employed to determine the link adaptationto be applied to data transmissions on a wireless channel.

A further aspect of the invention is the use of some (re)ordering schemethat is reordering the channel quality measures prior to theirtransmission as channel quality information. According to this aspectthe channel quality measures of a channel may be (re)ordered so thatencoding of the measures yields the most accurate reconstruction of themeasures at the receiver. The (re)ordering mechanism may also becombined with the other aspects of the invention outlined above.

According to one exemplary embodiment of the invention a method fortransmitting channel quality information in a communication system isprovided. In this method the channel quality values (e.g., of theplurality of resource units) may be first partitioned into at least twopartitions. Then the channel quality values of at least one of the atleast two partitions may be transformed to obtain channel qualitycoefficients. These coefficients may be encoded to obtain signallinginformation on the channel quality which is signalled to a receivingentity.

In one embodiment, the number of the channel quality coefficientsobtained for a respective partition by transformation is equal to thenumber of the channel quality values of the respective partition.

Further, the transformation used for transforming of the channel qualityvalues may for example be a discrete cosine transformation (DCT), aFourier transformation or a transformation based on a continuousfunction.

Another embodiment of the invention relates to situations where thechannel quality values are encoded. Channel quality information may betransmitted in a communication system by first partitioning channelquality values of the plurality of resource units into at least twopartitions, encoding the channel quality values to obtain signallinginformation on the channel quality and signalling the signallinginformation on the channel quality to a receiving entity.

In one embodiment, the channel quality values may be partitioned bycomparing the individual channel quality values to at least one channelquality threshold value. Typically, one threshold value per boundary ofneighboring partitions may be defined.

Further, in another embodiment the channel quality values arepartitioned by allocating a given number of channel quality values to arespective partition. This number of channel quality values in apartition may for example be preconfigured. The predefinition of thenumber of values per partition may for example be advantageous in thatno signalling of the number of elements in the partition is necessary.

Typically, it may also be advantageous if the sum of the cardinality ofthe at least two partitions is equal to the number of channel qualityvalues, i.e., all channel quality values are allocated to either one ofthe at least two partitions.

In a further embodiment of the invention, the channel qualitycoefficients or values may be encoded by compressing the channel qualitycoefficients or values, respectively, of at least one partition.

In one embodiment, the signalling information on the channel quality mayindicate a number of encoded channel quality coefficients or values tothe receiving entity that is smaller than the number of the channelquality coefficients or values, respectively, in the at least twopartitions. Thereby, according to an exemplary variation of thisembodiment, the channel quality coefficients or values are encoded byselecting the minimum number of channel quality coefficients or values,respectively, from a partition yielding a power level equal to or higherthan a threshold power level.

According to another embodiment of the invention, the channel qualitycoefficients or values may be encoded by selecting a subset of thechannel quality coefficients or values, respectively, from at least twopartitions. Thereby, according to an exemplary variation of theembodiment, the cardinality of a first subset of the subsets may dependon the cardinality of a second subset of the subsets.

In another embodiment of the invention, it is suggested that prior toencoding at least one combined channel quality coefficient or valuederived from at least two channel quality coefficients or values,respectively, is determined and that the at least one combined channelquality coefficient or value is encoded. This may for example be usefulin order to reduce the signalling overhead by combining all or a subsetof channel quality values/coefficients to one or more averagedvalues/coefficients prior to transmission.

Another option to encode the channel quality values or coefficientsaccording to another embodiment of the invention is to encode same byselecting a predefined number of channel quality coefficients or values,respectively, from the at least two partitions. Thereby, the number ofselected channel quality coefficients or values from a first partitionof the at least two partitions may for example depend on at least onepredetermined constraint, while the remaining number of selected channelquality coefficients or values may be selected from at least the secondpartition of the at least two partitions.

Generally, the partitions may be encoded according to the same oraccording to different encoding schemes.

Moreover, in another embodiment of the invention, the channel qualitycoefficients or values of at least two partitions may be jointlyencoded. This may for example be implemented as follows. A respectivechannel quality coefficient or value in a respective partition may beidentified by an index. The channel quality coefficients or values maybe jointly encoded by selecting channel quality coefficients or values,respectively, from at least two partitions having the same indices.

If the at least two partitions do not have equal cardinality, it may bebeneficial to add padding coefficients or values to a partition so as toobtain at least two partitions having same cardinality.

In another embodiment, a respective channel quality coefficient or valuein a respective partition may be indexed. In this embodiment averagedchannel quality coefficients or values are determined prior to encodingand the averaged channel quality coefficients or values are encoded.

For example, the averaged channel quality coefficients or values may bedetermined by a coefficient-wise or value-wise averaging of channelquality coefficients or values, respectively from at least twopartitions. Further, it may be foreseen that channel qualitycoefficients or values, respectively from at least two partitions havingthe same index are averaged coefficient-wise or value-wise,respectively. This may for example allow for reducing the indexsignalling overhead.

In another embodiment of the invention, the channel quality coefficientsor values of at least one partition may be reordered prior to theirencoding. For example, reordering is performed according to one ofpredefined reordering maps or according to one of predefinedinterleaving schemes.

As indicated previously, a respective channel quality coefficient orvalue in a respective partition may be identified by an index. In afurther embodiment of the invention the signalling information on thechannel quality may indicate the indices of the encoded channel qualitycoefficients or values of a respective partition included in thesignalling information on the channel quality. In a variation of thisembodiment, the signalling information on the channel quality mayfurther comprise information on the values of the encoded channelquality coefficients or values.

According to another embodiment of the invention, at least one of the atleast two partitions may be partitioned prior to transformation orencoding to obtain at least two sub-partitions. This may be useful insituations where for example a first partitioning is performed accordingto the number of antennas (e.g., one partition of channel quality valuesper antenna) and then each of the partitions is again divided intosub-partitions (e.g., based on a threshold value). Further, the channelquality values in at least one sub-partition may by transformed prior toencoding to obtain channel quality coefficients for a respectivesub-partition.

Another embodiment of the invention relates to a method forreconstructing channel quality values. According to this method areceiving entity may receive signalling information on the channelquality from a transmitting entity. This signalling information on thechannel quality may be decoded by the receiving entity to obtain channelquality coefficients of at least two partitions. Further, the channelquality coefficients of each partition may be transformed to obtainchannel quality values for a respective partition, and the channelquality values may be reconstructed using the channel quality values ofat least one partition.

According to another embodiment, no (inverse) transformation of channelquality coefficients may be necessary, e.g., due to performing notransformation on the transmitting entity side. In these cases thechannel quality values may be directly derived from the signallinginformation on the channel.

In a further embodiment, the channel quality values of the plurality ofresource units may be received from a plurality of transmittingentities. According to this embodiment, the receiver schedules arespective one (at least one) of the plurality of transmitting entitiestaking into account at least the reconstructed channel quality valuessignalled by the respective transmitting entity.

In another embodiment, the receiver may select at least one linkadaptation parameter for link adaptation for a respective one of theplurality of transmitting entities taking into account at least thereconstructed channel quality values signalled by the respectivetransmitting entity. For example, this at least one link adaptationparameter may be related to at least one of a modulation and codingscheme, a configuration of at least one hybrid automatic repeat requestprocess, and transmission power control.

Further, according to another embodiment, a management entity maydetermine at least one parameter for at least one of partitioning,encoding, or transformation. Moreover, the management entity may conveythe at least one parameter to the channel quality informationtransmitter using a control signal. For example, the management entitymay be a base station (Node B in the UMTS terminology) or may be anothernetwork entity located in the core network or access network of acommunication system.

Another embodiment of the invention provides a transmitter fortransmitting channel quality information in a communication system. Thistransmitter may comprise a processing unit for partitioning channelquality values into at least two partitions. The processing may furthertransform the channel quality values of at least one of the at least twopartitions to obtain channel quality coefficients. The transmitter mayalso include a coding unit for encoding the channel quality coefficientsto obtain signalling information on the channel quality and atransmitting unit for signalling the signalling information on thechannel quality to a receiving entity.

A further embodiment of the invention relates to a transmittercomprising a processing unit for partitioning channel quality values ofthe plurality of resource units into at least two partitions, and acoding unit for encoding the channel quality values to obtain signallinginformation on the channel quality. Further, the transmitter maycomprise a transmitting unit for signalling the signalling informationon the channel quality to a receiving entity.

Furthermore, in another embodiment the transmitter may have means toperform the steps of the method for transmitting channel qualityinformation in a communication system according to one of the variousembodiments described herein.

According to another embodiment, a receiver for reconstructing channelquality values is provided. The receiver may comprise a receiving unitfor receiving signalling information on the channel quality from atransmitting entity. Further, the receiver may have a decoding unit fordecoding the signalling information on the channel quality to obtainchannel quality coefficients of at least two partitions, and aprocessing unit for transforming the channel quality coefficients ofeach partition to obtain channel quality values for a respectivepartition. The processing unit may reconstruct the channel qualityvalues using the channel quality values of at least one partition.

In another embodiment, a receiver for reconstructing channel qualityvalues may comprise a receiving unit for receiving signallinginformation on the channel quality from a transmitting entity, and adecoding unit for decoding the signalling information on the channelquality to obtain channel quality values of at least two partitions.Moreover, the receiver according to this embodiment may comprise aprocessing unit for reconstructing the channel quality values of aplurality of resource units using the channel quality values of at leastone partition.

Furthermore, in another embodiment the receiver may contain means toperform the steps of the method for reconstructing channel qualityvalues according to one of the various embodiments described herein.

Another embodiment of the invention relates to a computer-readablemedium storing instructions that, when executed by processor of atransmitter, cause the transmitter to transmit channel qualityinformation in a communication system. The transmitter may be caused totransmit channel quality information in a communication system bypartitioning channel quality values into at least two partitions,transforming the channel quality values of at least one of the at leasttwo partitions to obtain channel quality coefficients, encoding thechannel quality coefficients to obtain signalling information on thechannel quality and signalling the signalling information on the channelquality to a receiving entity.

In another embodiment, a transmitter may be caused to transmit channelquality information in a communication system by partitioning channelquality values into at least two partitions, encoding the channelquality values to obtain signalling information on the channel qualityand signalling the signalling information on the channel quality to areceiving entity.

A further embodiment relates to a computer-readable medium storinginstruction that, when executed by the processor of the transmittercause the transmitter to perform the steps of the method fortransmitting channel quality values according to one of the variousembodiments described herein.

Another computer-readable medium according to an embodiment of theinvention stores instruction that, when executed by a processor of areceiver, cause the receiver to reconstruct channel quality values.

The receiver may be caused to reconstruct channel quality values byreceiving signalling information on the channel quality from atransmitting entity, decoding the signalling information on the channelquality to obtain channel quality coefficients of at least twopartitions, and transforming the channel quality coefficients of eachpartition to obtain channel quality values for a respective partition,and reconstructing the channel quality values of the plurality ofresource units using the channel quality values of at least onepartition.

In another embodiment, the receiver may be caused to reconstruct channelquality values by receiving signalling information on the channelquality from a transmitting entity, decoding the signalling informationon the channel quality to obtain channel quality values of at least twopartitions, and reconstructing the channel quality values of theplurality of resource units by using the channel quality values of atleast one partition.

A further embodiment relates to a computer-readable medium storinginstruction that, when executed by the processor of the receiver causethe receiver to perform the steps of the method for receiving channelquality information in a communication system according to one of thevarious embodiments described herein.

Another embodiment of the invention relates to a method for transmittingchannel quality information in a communication system. The transmittingentity may reorder channel quality values, and may then transform thereordered channel quality values to obtain channel quality coefficients.Further, the channel quality coefficients may be encoded to obtainsignalling information on the channel quality which may be signalled toa receiving entity.

In a further embodiment, the reordering comprises determining a numberof sequences of reordered channel quality values by employing differentreordering mappings. Moreover, the transmitting entity may choose areordering mapping for which the reordered channel quality valuesfulfill an optimality criterion prior or after transformation.

Furthermore, in another embodiment of the invention, the reorderingscheme is signalled to the receiving entity, for example, within thechannel quality information.

In another embodiment, the reordering mappings are defined by at leastone reordering parameter.

A further embodiment of the invention relates to a method forreconstructing channel quality values. A receiving entity may firstreceive signalling information on the channel quality from atransmitting entity and may decode the signalling information on thechannel quality to obtain channel quality coefficients. The receivingentity may transform the channel quality coefficients, and reconstructchannel quality values by reordering the transformed channel qualitycoefficients.

Thereby, another embodiment foresees that the transformed channelquality coefficients are reordered according to a mapping scheme. Themapping scheme may, for example, be indicated within the channel qualityinformation or in control signalling received by the receiving entity.

Another embodiment of the invention relates to a transmitter fortransmitting channel quality information in a communication system. Thetransmitter comprises a reordering unit for reordering channel qualityvalues, and a processing unit for transforming the reordered channelquality values to obtain channel quality coefficients. Further, a codingunit of the transmitter may encode the channel quality coefficients toobtain signalling information on the channel quality and a transmissionunit may signal the signalling information on the channel quality to areceiving entity.

Another embodiment relates to a receiver for reconstructing channelquality values. The receiver may include a receiving unit for receivingsignalling information on the channel quality from a transmitter, andfurther a decoding unit for decoding the signalling information on thechannel quality to obtain channel quality coefficients. The receiver mayalso comprise a processing unit for transforming the channel qualitycoefficients, and a reordering unit for reconstructing channel qualityvalues by reordering the transformed channel quality coefficients.

Another embodiment of the invention relates to a computer readablemedium storing instruction that, when executed by a processor of atransmitter, cause the transmitter to transmit channel qualityinformation in a communication system, by reordering channel qualityvalues, transforming the reordered channel quality values to obtainchannel quality coefficients, encoding the channel quality coefficientsto obtain signalling information on the channel quality and signallingthe signalling information on the channel quality to a receiving entity.

A further embodiment of the invention relates to a computer readablemedium storing instruction that, when executed by a processor of areceiver, cause the receiver to transmit channel quality information ina communication system, by receiving signalling information on thechannel quality from a transmitter, decoding the signalling informationon the channel quality to obtain channel quality coefficients,transforming the channel quality coefficients, and reconstructingchannel quality values by reordering the transformed channel qualitycoefficients

BRIEF DESCRIPTION OF THE FIGURES

In the following the invention is described in more detail in referenceto the attached figures and drawings. Similar or corresponding detailsin the figures are marked with the same reference numerals.

FIG. 1 shows an exemplary channel structure of an OFDMA system and adynamic allocation of radio resources on a transmission time intervalbasis to different users, and

FIG. 2 shows an exemplary data transmission to users in an OFDMA systemin localized mode (LM) having a distributed mapping of Layer 1/Layer 2control signalling,

FIG. 3 shows an exemplary data transmission to users in an OFDMA systemin distributed mode (DM) having a distributed mapping of Layer 1/Layer 2control signalling,

FIG. 4 shows a flow chart of a method for transmitting channel qualityinformation according to an embodiment of the invention,

FIG. 5 shows a flow chart of a method for transmitting channel qualityinformation according to an embodiment of the invention, wherein notransformation of channel quality values is performed,

FIG. 6 shows a flow chart of a method for reconstructing channel qualityvalues of a channel from received channel quality information accordingto an embodiment of the invention,

FIG. 7 shows a flow chart of a method for reconstructing channel qualityvalues of a channel from received channel quality information accordingto an embodiment of the invention, wherein no transformation of channelquality coefficients to channel quality values is performed,

FIG. 8 shows an exemplary snapshot of channel quality values (here“power”) for a sequence of 24 resource blocks for a radio channel, andthe corresponding reconstruction using compressed Strongest 5 DCTtransmission,

FIG. 9 shows the full DCT and the strongest 5 DCT components for thechannel in FIG. 8,

FIG. 10 shows a bitmap to indicate which DCT coefficients are thestrongest according to FIG. 9,

FIG. 11 shows an exemplary snapshot of channel power values for asequence of 24 resource blocks for a radio channel, and thecorresponding reconstruction using a “Best 5 Individual” compression ofthe channel quality values,

FIG. 12 shows an exemplary snapshot of channel power values for asequence of 24 resource blocks for a radio channel, and thecorresponding reconstruction using a “Best 5 Average” compression of thechannel quality values,

FIG. 13 shows a bitmap to indicate which resource blocks have the best(strongest) channel quality values in FIG. 11 and FIG. 12,

FIG. 14 shows an exemplary categorization of channel quality measures(here “power”) of a plurality of resource units of a channel into twopartitions according to an exemplary embodiment of the invention,

FIG. 15 shows an exemplary bitmap for signalling the affiliation ofresource units to partition for FIG. 14 according to an exemplaryembodiment of the invention, where a “1” denotes affiliation to a firstpartition and a “0” denotes affiliation to a second partition,

FIG. 16 shows the result of partition-wise DCT for the first partitionof channel quality values from FIG. 14, and indicates the threestrongest DCT components that may be chosen for transmission, accordingto an exemplary embodiment of the invention,

FIG. 17 shows the result of partition-wise DCT for the second partitionof channel quality values from FIG. 14, and indicates the threestrongest DCT components that may be chosen for transmission, accordingto an exemplary embodiment of the invention,

FIG. 18 shows an exemplary bitmap for signalling which DCT componentsare transmitted for the first partition with respect to thestrongest-three criterion according to FIG. 16 according to an exemplaryembodiment of the invention,

FIG. 19 shows an exemplary bitmap for signalling which DCT componentsare transmitted for the second partition with respect to thestrongest-three criterion according to FIG. 17 according to an exemplaryembodiment of the invention,

FIG. 20 shows the channel state as in FIG. 14 and a reconstruction ofchannel quality values from compressed partition-wise DCT according toan exemplary embodiment of the invention,

FIG. 21 shows the channel state as in FIG. 14 and a reconstruction ofchannel quality values from compressed partition-wise DCT with reducedcoefficient signalling overhead according to an exemplary embodiment ofthe invention,

FIG. 22 shows an example of an original sequence consisting of only twodistinct SINR values, and the corresponding DCT transform,

FIG. 23 shows an example how the resource blocks of FIG. 22 may begrouped into two partitions according to an exemplary embodiment of theinvention,

FIG. 24 shows the result of partitioning the resource blocks of FIG. 22into partition 1, and the corresponding DCT transform of partition 1,according to an exemplary embodiment of the invention,

FIG. 25 shows an exemplary bitmap for signalling the strongest DCTcomponent of the partition 1 DCT of FIG. 22, according to an exemplaryembodiment of the invention,

FIG. 26 shows the result of partitioning the resource blocks of FIG. 22into partition 2, and the corresponding DCT transform of partition 2according to an exemplary embodiment of the invention,

FIG. 27 shows the bitmap to signal the strongest DCT component of thepartition 2 DCT of FIG. 22 according to an exemplary embodiment of theinvention,

FIG. 28 shows a mobile communication system according to one embodimentof the invention, in which the ideas of the invention may beimplemented,

FIG. 29 shows an exemplary flow chart of a method for transmittingchannel quality information using a reordering (re)mechanisms accordingto an embodiment of the invention and

FIG. 30 shows another exemplary flow chart of a method for transmittingchannel quality information using a reordering (re)mechanisms andtransformation of the channel quality values according to anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Before outlining the concepts and the ideas of the invention accordingto different embodiments in further detail, the following notation usedherein should be recognized:

-   N_(rb) denotes the total number of resource unit of a channel,-   v_(i) or v_(i) ^(j) denotes a channel quality value i for resource    unit i, where i=1, K, N_(RB), j may indicate the partition P_(j) to    which the channel quality value has been assigned-   N_(P) _(i) denotes the number of channel quality values in partition    P_(i)

P_(i) = {v₁^(i), K, v_(N_(P_(i)))^(i)}

denotes a set or partition having N_(p) _(i) channel quality values

-   c_(i) or c_(i) ^(j) denotes a channel quality coefficient i, j may    indicate the transformed partition T_(j) of the channel quality    coefficient-   N_(T) _(i) denotes the number of channel quality coefficients in a    set or transformed partition T_(i)

T_(i) = {c₁^(i), K, c_(N_(T_(i)))^(i)}

denotes a set or transformed partition having N_(T) _(i) channel qualitycoefficients obtained by transforming partition P_(i)

-   N_(r) denoted the total number of defined (re)ordering algorithms-   N_(MIMO) denotes the total number of MIMO data streams-   M_(o) denotes the number of channel quality values or coefficients    transmitted for all partitions-   M_(i) denotes the number of transmitted channel quality values for    partition Pi or the number of transmitted channel quality    coefficients for transformed partition T_(i)-   M_(s) denotes the sum of transmitted (e.g., after compression)    coefficients for all partitions-   A_(i) denotes parent partition A-   B_(i,j) denotes sub-partition j belonging to parent partition A_(i)-   D denotes the number of bits used for transmission of a single    channel quality value v_(i) or channel quality coefficient c_(i)

$\begin{pmatrix}n \\k\end{pmatrix}\mspace{14mu} {means}\mspace{14mu} \frac{n!}{{k!} \cdot {\left( {n - k} \right)!}}$

-   ┌x┐ is the smallest integer number that is equal to or greater than    x

Id(x)=log₂(x) denotes the logarithm of x having base 2

Generally it should be further noted that the term “compression” as usedherein refers to a channel quality information provision scheme, wherethe total channel quality information feedback overhead is reducedcompared to the “Full Feedback” case described in the TechnicalBackground section.

Further, it should be noted that the term “resource unit” as used hereinrefers to one of a plurality of resource units of a channel for which achannel quality measure is obtained. Channel quality reporting may thusbe performed on a per-resource unit basis. Moreover, this resource unitmay or may not be equal to a resource block denoting the smallest amountof resources of a channel that can be allocated to a user (e.g., byscheduling). For example in an OFDMA system, a resource unit could referto a resource of one subframe in the time domain and a subband in thefrequency domain, while a resource block denotes a subframe in the timedomain and a subcarrier (of one of the subbands) in the frequencydomain. In another embodiment of the invention, a resource unit refersto a range of time or frequencies (sub carriers)—in time or frequencydomain—over which the channel state is substantially flat, e.g., acoherence time or coherence bandwidth, which may or may not be amultiple of the respective smallest amount of resources in thecommunication system (e.g., resource block, subframe, TTI).

As can be already recognized from this summary of the variables andsymbols as used herein, most of the embodiments outlined herein considerfor exemplary purposes the transmission of channel quality informationfor a channel (e.g., shared channel) in communication systems. Hence,some of the exemplary embodiments described in the sequel assume amobile communication system as described in the Technical Backgroundsection above.

The invention relates to the communication of information on the stateof a channel between a transmitting entity and a receiving entity, suchas for example a mobile station and a base station in a mobilecommunication system. A resource management entity preferably has somesort of channel state information available for the link between basestation and mobile station (“downlink”) as well as for the link betweenmobile station and base station (“uplink”). Assuming that this resourcemanagement entity is located within the base station or farther towardsthe network side, the channel state information for the downlink mayhave to be measured by the mobile station and then be transmitted viathe uplink to the base station to the resource management entity.Conversely, if said resource management entity is located within themobile station or farther at the user equipment side, the channel stateinformation for the uplink may have to be measured by the base stationand then be transmitted via the downlink to the mobile station to theresource management entity. In some embodiments the channel statemeasures (or channel quality values) are provided or measured for eachresource unit into which the communication channel between transmittingentity and receiving entity is divided.

One aspect of the invention is to divide the channel state measures intodistinct partitions—in case of having a channel quality measure perresource unit this can also be viewed as a partitioning of the resourceunits. Each partition consists only of a subset of the channel statemeasures. The partitioning of the channel quality feedback measures mayallow for reducing the amount of overhead that needs to be attributed tothe signalling of channel quality information, as (in some embodiments)the portioning may be advantageously used to further reduce the amountof signalling information. Further, the partitioning of the channelquality measures may allow for a more accurate reconstruction of thechannel state at the receiver.

Another aspect of the invention relates to the receiver that inverts thecompression scheme to reconstruct the channel quality measures. In someexemplary embodiments of the invention, a scheduler may utilize theinformation on the channel condition to schedule air interface resourcesof transmitters that are served by the scheduler. Moreover,alternatively or in addition thereto, the reconstructed channel estimatemay also be employed to determine the link adaptation to be applied todata transmissions on a wireless channel.

A further aspect of the invention is the use of some sort of(re)ordering scheme that is reordering the channel quality measuresprior to their transmission as channel quality information. For example,the reordering of the channel quality measures may be obtained by aninterleaving algorithm. According to this aspect the channel qualitymeasures of a channel may be (re)ordered so that encoding of themeasures yields the most accurate reconstruction of the measures at thereceiver. For example, if transforming the channel quality measures andtransmitting a subset of the resulting channel quality coefficients, the(re)ordering prior to the transformation may be chosen so as toconcentrate most power of the channel quality measures in a number ofcoefficients that can be transmitted according to the encoding scheme.The (re)ordering mechanism may be combined with the other aspects of theinvention as will be outlined in further detail in the following.

It may be advantageous but not a prerequisite that in multi-usercommunication systems the channel quality feedback is most accurate forthe strongest resources. The channel quality may be periodicallymeasured or determined by a reporting terminal. Generally, this may, forexample, be implemented by measuring the channel quality for each of aplurality of resource units into which the communication channel toreport on is (logically) divided at the reporting terminal to obtain aset of channel quality values or measures (e.g., power values).

FIG. 4 shows a flow chart of a method for transmitting channel qualityinformation according to an embodiment of the invention. In a first stepthe transmitting entity may determine 401 the channel quality measuresof the channel. This may, for example, be accomplished by measuring achannel quality value for each resource unit of the channel on which thetransmitting entity is reporting. An exemplary channel snapshot obtainedby the measurement is shown in FIG. 14. For exemplary purposes only itis assumed that the channel on which is to be reported is divided into24 resource units for which individual channel quality measures aredetermined. As a result of this channel quality determination procedure24 channel quality values v₁, K, v₂₄ are obtained.

Next, an unequal accuracy approach by creating 402 at least twopartitions of resource units is used. Each resource unit i.e., itschannel quality measure may be assigned unambiguously to exactly onepartition. The partitions may, for example, be defined such thatresource units with similar channel quality measures (e.g., powervalues) are contained in the same partition.

In one exemplary embodiment, only the resource units having thestrongest channel quality values (e.g., power values) are contained in afirst partition, and other resource units are contained within a secondpartition. In the example of FIG. 14, the following partitions arecreated:

P₁ = {v₈¹, v₉¹, v₁₀¹, v₁₈¹, v₁₉¹}  andP₂ = {v₁², K, v₇², v₁₁², K, v₁₇², v₂₀², K, v₂₄²}

In this example, the partition creation is depending on e.g., one ormore partition threshold values. FIG. 14 shows an example of thepartition threshold to define a first and a second partition, each ofwhich contains only resource units whose SINR is either above or belowthe threshold value, respectively. It is a matter of convention whetherresource units that have SINR values equal to the threshold should gointo the first or into the second partition.

Typically the partitions are each of cardinality smaller than that ofthe original sequence. Without loss of generality, it may be assumedthat the number of elements in the first partition N₁ is smaller than orequal to the number of resource units in the original sequence N_(rb).

Preferably, the channel quality values of the resource units are orderedin the same way as is the original sequence. Therefore following theexample of FIG. 14, the first partition P₁ should consist of the channelquality values with the indices 8, 9, 10, 18, 19 (i.e., v₈ ¹, v₉ ¹, v₁₀¹, v₁₈ ¹, v₁₉ ¹) of the original sequence in that order, while thesecond partition should consist of the channel quality values with theindices 1-7, 11-17, 20-24 of the original sequence (i.e., v₁ ², K, v₇ ²,v₁₁ ², K, v₁₇ ², v₂₀ ², K, v₂₄ ²) in that order. Therefore thecardinality of the first partition is five (N₁=5), and the cardinalityof the second sequence is nineteen (N₂=19). The sum is therefore thecardinality of the original sequence, twenty-four in this

case (N₁+N₂=N_(rb)=24).

Evidently, when partitioning the channel quality values v₁, K, v₂₄according to this example, the sum of the number of elements in eachpartition is equal to the number of resource units in the originalsequence. The partitioning (partition affiliation) of the channelquality measures may be represented by a bitmap as illustrated in FIG.15, where the partition to which a respective channel quality measure isassigned is indicated by a single bit. Obviously, more bits per channelquality measure are needed if more than two partitions are formed (e.g.,┌ld(n)┐ bits for n partitions).

This example is also shown in FIG. 14 where a partition threshold isused to divide the 24 channel quality measures into two partitions. Aswill become more apparent from the following description, there existmultiple schemes how to partition the channel quality measures into atleast two partitions. For example, in another embodiment, the number ofelements that should go into each partition is known before thepartition creation process. This will obviate the necessity to informthe receiver of the number of elements that belong to a partition.

In a next step 403, the channel quality values in at least one of thetwo created partitions are transformed. For example, according to oneembodiment of the invention, a discrete cosine transform for eachpartition (P₁ and P₂) is performed. Details on a DCT as may be used byin an embodiment of the invention may be found in Ahmed, N., NatarajanT. and Rao K. R., “Discrete Cosine Transform”, IEEE Trans. Computers,January 1974 incorporated herein by reference.

As a result the transformed partitions T₁ and T₂ are obtained.Typically, the DCT does not change the number of elements in a set,i.e., the cardinality of the transform is equal to the cardinality ofthe source. Consequently in the example of FIG. 14, FIG. 16 and FIG. 17,the DCT of the first partition T₁ contains five elements, while the DCTof the second partition T₂ contains nineteen elements, as visualized inFIG. 16 and FIG. 17. Nevertheless, it should be noted that it is notnecessary to always calculate a number of coefficients equal to thenumber of elements contained in the set to be transformed. In someembodiments, fewer coefficients than elements in the set to betransformed are calculated. This may, for example, be useful in anencoding scheme where only the first M coefficients of a transformationare transmitted.

In step 404, the channel quality coefficients obtained by thetransformation in step 403 are encoded. In one exemplary embodiment ofthe invention, this may be accomplished by performing a compression ofthe coefficients for each transformed partition T_(i) separately.

For example, in each transformed partition only certain DCT coefficientsare selected for feedback transmission. Generally, the number of DCTcoefficients selected for transmission M_(i) is dependent on thepartition number i. In the example shown in FIG. 16 and FIG. 17, thesenumbers have been chosen as M₁=M₂=3.

Alternatively, compression may take the coefficients of at least twotransformed partitions into account. In this example, the total numberof DCT coefficients to be transmitted after compression (e.g., the sumM₁+M₂ for two partitions) is a (pre)determined or preconfigured value.

Alternatively, compression may take the number of available bits forchannel quality information transmission of at least two transformedpartitions into account. In this example, the total number of availablebits for the channel quality information transmission compression aftercompression is a (pre)determined or preconfigured value. The number oftransmitted DCT coefficients after compression per partition may then bedetermined taking the required signalling for at least two partitionsinto account, plus the necessary amount of bits for partitionaffiliation or coefficient index signalling, if required. A similarapproach may also be used when “directly” compressing the channelquality values, i.e., when not performing a transformation of thepartition(s).

The mobile terminal may determine how many DCT coefficients from eachtransformed partition are selected for transmission and under whichconstraint(s) the selection is performed. If, for example, the valueswithin a transformed partition are constant or nearly constant, then oneor two DCT coefficients are sufficient for reconstruction at thereceiver. Consequently the mobile station may transmit more DCTcoefficients of another partition that shows greater fluctuations in itsDCT coefficients.

Since the transmitter, e.g., the mobile station, has the most accuratechannel information, it may deliberate within the above constraints,depending on the actual channel conditions, how to use the availablenumber of coefficients or bits to convey the optimum accuracy to thereceiving entity. The constraints could be further defined to require aminimum number of coefficients for a given partition, limiting thedegree of freedom of the mobile terminal. This method may howeverrequire additional signalling of the selected coefficients from themobile station to the receiving entity.

In one embodiment of the invention, the coefficients are chosenaccording to their absolute values or according to their squaredabsolute value. In another embodiment, the coefficients are chosen suchthat in each partition the selected coefficients contain at least athreshold amount of power of the whole partition. In an example, sincethe first (transformed) partition T₁ may be more important than thesecond (transformed) partition T₂, it may be beneficial to select asmany coefficients from the first partition T₁ so that the selectedcoefficients contain more than a partition threshold value ofP_(threshold) e.g., more than P_(threshold)=99%, of the total powercontained in the first partition T₁. If more coefficients are requiredfor this criterion than available in the first partition T₁, thestrongest coefficients of partition T₁ should be selected. If fewercoefficients than available are required for this criterion, then theremaining coefficients may be employed to select an appropriate numberof coefficients from the second partition T₂. Obviously, otherconstraints like those mentioned above (e.g., minimum number of selectedcoefficients per partition) may further reduce the degree of freedom.

For example, the DCT coefficients for the first partition T₁ accordingto FIG. 16 (obtained by squaring and normalization) respectively contain98.07%, 0.41%, 0.02%, 0.5%, and 1% of the total power. Consequently tocapture more than 99% of the power, the selection of coefficients 1 and5 (i.e., c₁ ¹ and c₅ ¹) of partition T₁ may be sufficient. Assuming thata total number of 6 coefficients can be selected for transmission in theencoding procedure 404, the remaining 4 coefficients can then beselected from the second partition (see FIG. 17). To save signalling forthe second partition, the first four coefficients of the secondpartition T₂ may be selected by default. For higher accuracy, the fourstrongest coefficients of partition T₂ may be selected. In this fashion,coefficients 1, 3, 10, and 11 (i.e., c₁ ², c₃ ², c₃ ², and c₁₁ ²) may beselected in the example. These coefficients contain almost 88% of thepower of partition T₂.

Without using this threshold power criterion for selecting thecoefficients from the transformed partitions for transmission, the powercontained in the selection for partition T₁ is 99.57% (i.e., a gain of0.5%), while for partition T₂ it is only roughly 85.38% (i.e., a loss ofabout 2.5%) given that three strongest coefficients from each partitionare chosen. Depending on the constraints imposed by the communicationsystem, those skilled in the art will be able to select the most suitedcoefficients from the partitions as needed.

Next, in step 405 the selected channel quality coefficients from thepartitions are transmitted as channel quality information to thereceiving entity. Depending on the encoding scheme it may also benecessary to encode information indicating the partitioning (partitionaffiliation) of the channel quality values at the transmitter, forexample, by means of a bit pattern as shown in FIG. 15. Further, if nopreconfigured coefficients from the partitions are selected it may benecessary to further inform the receiver which coefficients arecommunicated by signalling the indices of coefficients (coefficientindex signalling) included in the channel quality information.

FIG. 5 shows another exemplary flow chart of a method for transmittingchannel quality information according to an embodiment of the invention.Essentially, the flow chart shown in FIG. 5 is similar to same in FIG.4. In contrast to the scheme outlined with respect to FIG. 4 above, thechannel quality information transmission scheme shown in FIG. 5 does notinclude a transformation of the partitions P₁ and P₂ prior to encoding.Instead, the channel quality values v_(i) of the respective partitionsmay be directly encoded 501 using similar mechanisms as described withrespect to FIG. 4 above and are subsequently transmitted 502 as channelquality information to the receiver.

Next the reconstruction of the channel quality information at thereceiving entity will be discussed with respect to FIG. 6 and FIG. 7.FIG. 6 shows an exemplary flow chart of a method for receiving andreconstructing channel quality values for channel quality informationaccording to an embodiment of the invention.

FIG. 6 essentially mirrors the steps of FIG. 4 at the receiving entity.First, the channel quality information provided by a transmitter (e.g.,a mobile station) is received 601 at the receiver such as a base stationhaving scheduling and/or link adaptation functionality. The channelquality information may then be decoded 602. This means that the channelquality coefficient values (and optionally the indices for the signalledchannel quality coefficient values) in the channel quality informationare used to first reconstruct the channel quality coefficients that havebeen selected by the transmitter for transmission in terms of theirvalues and position.

Further, the partitions T_(i) may be reconstructed 603 based on thepartitioning pattern (partition affiliation) in the channel qualityinformation received from the transmitter. Thereby the respectivecoefficients in the partitions may be either set according to thesignalled coefficient values or to zero (or a predetermined value) if acoefficient value is not signalled in the channel quality information.

Upon having reconstructed the partitions T_(i) same may be transformed604 to reconstruct partitions P_(i) of channel quality values. Thepartitions P_(i) of channel quality values are subsequently combined toreconstruct the set of channel quality measures v₁, K, v₂₄ at thereceiver for the plurality of resource units.

FIG. 7 shows another exemplary flow chart of a method for receiving andreconstructing channel quality values for channel quality informationaccording to an embodiment of the invention. Essentially, the individualsteps shown in FIG. 7 are similar to those shown in FIG. 6. However, asin FIG. 5, it is assumed that the channel quality values of thepartitions P_(i) are directly encoded and transmitted to the receiver.Hence, upon the reception of the partitions P_(i) of channel qualityvalues may be directly reconstructed 702 from the channel qualityinformation by a decoder in step 701.

FIG. 20 shows the channel state as in FIG. 14 and a reconstruction ofchannel quality values from compressed partition-wise DCT according toan exemplary embodiment of the invention. The partitioning of thechannel quality values in two partitions and the partition-wise encodingof channel quality coefficients by selecting M₁=M₂=3 coefficients fromeach partition allows for an accurate reconstruction of the originalsequence of channel quality measures. It is especially worth noting thatfor the most important resource units (i.e., those having the highestchannel quality values) the reconstruction is very accurate.

The reason for the accurate reconstruction of the channel quality valuesfrom the channel quality information at the receiver when using one ofthe schemes according to the different embodiments of the invention willbe outlined in the following with respect to FIG. 22 to FIG. 27.

FIG. 22 shows an example of an original sequence consisting of only twodistinct SINR values, and the corresponding DCT transform. It should benoted that the presence of only two distinct channel quality values inthis example is only intended to illustrate the benefits of employingthe present invention. As can be seen from the DCT transformation of theoriginal sequence of channel quality values, there is a strong DCcomponent and several higher-index DCT coefficients representing asubstantial part of the power of the original sequence. Hence, thenumber of coefficients to represent a given power threshold value ofP_(threshold)=99% is significant and still implies a significantoverhead.

Partitioning the channel quality values shown in the upper part of FIG.22 into two partitions in this example allows for having a more regulardistribution of channel quality values in each of two partitions.Comparing the exemplary original sequence of channel quality values asin FIG. 22, two partitions may be created that comprise channel qualityvalues of resource units with values of 4 and 1, respectively.Consequently the first partition contains only elements of having achannel quality value equal to 4 as shown in FIG. 24 upper part (i.e.,elements v₁, v₂, v₄, v₆, v₈, v₉, v₁₁, v₁₃, v₁₅, v₁₈, v₂₁ of the originalsequence), while the second partition contains only elements having achannel quality value equal to 1 as shown in FIG. 26 upper part (i.e.,elements v₁, v₃, v₅, v₇, v₁₀, v₁₂, v₁₄, v₁₆, v₁₇, v₁₉, v₂₀, v₂₂ to v₂₄of the original sequence). The partitioning may either be achieved bydefining that the first partition should contain 10 elements and thesecond partition 14 elements, or a partition threshold of a valuebetween 1 and 4 may have been defined.

As can be seen from FIG. 24 and FIG. 26, the distribution of channelquality values in each of the partitions is more regular in comparisonto the original sequence shown in FIG. 22. Due to this more regulardistribution of the channel quality values in the two partitions (inthis example a uniform distribution is obtained), the power of the DCTcoefficients of each of the two partitions shown in FIG. 24 and FIG. 26in the lower part, respectively, may be concentrated in the firstcoefficients of the DCT transform. In this example, due to the uniformdistribution of the values in each partition, the total power of thechannel quality values of a partition concentrates in the DC componentof the DCT transform as can be also seen from the bitmaps indicating thestrongest coefficients shown in FIG. 25 and FIG. 27 respectively.

This effect allows in turn reducing the number of coefficients that needto be transmitted. In the example, it is sufficient to transmit thevalue of the DC component of the DCT transform (i.e., the firstcoefficient) of each partition as well as information on thepartitioning (partition affiliation) of the values/coefficients (andoptionally the index of the transmitted DC component in the respectivepartition) to allow for an ideal reconstruction of the original sequenceof the channel quality values of FIG. 22 at the receiver. Thereby, theoverhead for transmitting these channel quality information to thereceiver may be less than in prior-art schemes.

In the subsequent sections several issues relating to the inventionaccording to one of the different embodiments will be discussed in thefollowing.

Transformation Scheme/Encoding Scheme

In the previous sections, it has been suggested to facilitate a bettercompression of the information to transmit by applying the DCT transformto the data in the individual partitions. Due to the nature of theconstituent cosine waveform, the use of a DCT may, for example, beparticularly applicable when the data in the partitions is of continuousnature or in cases of discrete nature of the data, if the discretevalues do not show large differences to each other. According to anotherembodiment, also other transformation schemes may be employed, such as,for example, the Fourier transform or other related continuousfunctions. Further, also other transform functions may be used, such asthe Haar transform, Hankel transform, Daubechies wavelet, etc. Use ofthe latter transforms may be advantageous, for example, in case of amore discrete nature of the data in the partitions (as it might be theresult of a coarse quantization of the channel quality values or aresult of mapping of the channel quality values onto modulation andcoding scheme (MCS) indices). Those skilled in the art will recognizethat the optimum compression transformation function will depend on thenature and properties of the data that is to be compressed.

In most embodiments of the invention discussed previously herein, allpartitions have been encoded or compressed using the sameencoding/compression scheme. Alternatively, each partition may employ acompression scheme independently from any other partition. For example,a first partition may be compressed employing the discrete cosinetransform, while another partition may be compressed using a Daubechieswavelet. From an implementation aspect however, it may be advantageousto employ the same compression approach in all partitions, so as tominimize the hardware or software efforts necessary.

Further according to another embodiment of the invention it may bebeneficial not to transform the channel state measures prior toencoding, but—for at least one partition—to compress the values directlyby transmitting only a subset of the values in a partition. This maylead to a kind of “Best M” compression, as outlined in the TechnicalBackground section, however, on a partition-basis.

It should be noted that the choice of transform or encoding schemes orparameters for at least one partition may vary over time. An option todetermine the transform or encoding scheme or parameters for at leastone partition may take the channel quality information reportingfrequency into account. For example, if channel quality informationreporting occurs infrequently (e.g., at a rate below a thresholdfrequency), it may be advantageous to transmit a large number ofvalues/coefficients to allow very detailed reconstruction, oralternatively to choose an encoding scheme that offers a high amount ofaccuracy such as “DCT Strongest M” or “Best M Individual”.

In contrast, if channel quality information reporting occurs frequently(e.g., at a rate equal to or above a threshold frequency), each channelquality information signal (message) may preferably be rather small, soas to keep the overall required amount of signalling small. This mayresult in the choice of a few number of values/coefficients or in thechoice of a quite coarse encoding scheme like “Average”, “Best MAverage”, or “DCT First M”.

In another embodiment, for a given first channel quality informationreporting frequency, a first transform or first encoding scheme or firstset of channel quality information transmission parameters (such asnumber of transmitted values/coefficients, number of partitions, numberof values in a partition, partition threshold values, etc.) is used. Forchannel quality information reports between two such channel qualityinformation reports, a second transform or second encoding scheme orsecond set of channel quality information transmission parameters isused.

Similarly, also in case the channel state changes significantly betweensuccessive reports (e.g., the difference between the total energy of oneor a plurality of channel quality measures at two time instants is abovea threshold) the transmitter may decide to transmit a large number ofvalues/coefficients to allow very detailed reconstruction, oralternatively to choose an encoding scheme that offers a high amount ofaccuracy.

Reordering

As outlined above, another aspect of the invention is the (re)orderingof channel quality values, for example, in combination with using anencoding scheme employing a transformation of the channel qualityvalues. FIG. 29 and FIG. 30 show exemplary flow charts of a method fortransmitting channel quality information using (re)ordering mechanismsaccording to different embodiments of the invention. While theembodiment shown in FIG. 29 does not employ partitioning andtransforming the channel quality values, the embodiment shown in FIG. 30further includes steps to transform the (re)ordered channel qualityvalues prior to transmission. It should be noted that in bothembodiments, also a partitioning of the channel quality values prior toor after (re)ordering may be foreseen.

As in FIG. 4 and FIG. 6, the channel quality values v₁, Λ, v_(N) _(rb)indicative of the channel quality may be either first measured 2901 ormay be available at the transmitter. Next, the channel quality valuesmay be (re)ordered 2902 to obtain a sequence of (re)ordered channelquality values v′₁, Λ, v′_(N) _(rb) . Subsequently, in the embodimentillustrated in FIG. 29, the (re)ordered channel quality values areencoded 2903 using one of the compression schemes described herein. Inthe embodiment shown in FIG. 30, the (re)ordered values may betransformed 3001, for example, using a DCT transformation as explainedabove first and are subsequently encoded 3002 using one of thecompression schemes described herein. The resulting channel qualityinformation is subsequently reported 2904, 3003 to the receiver.

The reordering in step 2902 may be done according to various differentmechanisms. For example, a known (re)ordering mechanism may be appliedthat is also known to the receiver. This would obviously require noadditional signalling overhead.

In another embodiment of the invention, a limited number N_(r) of(re)ordering mappings are determined, for example, by means of applyinginterleaving scheme(s) in a trial-and-error fashion. The transmitter mayobtain the reordered sequences of channel quality values using each ofthe defined (re)ordering algorithms prior to transformation, thusobtaining N_(r) reordered sequences. Out of these sequences, thetransmitter may choose one (re)ordered sequence for transmission (e.g.,after transformation and selection of the coefficients/values) thatfulfils a certain optimality criterion. Such an optimality criterionmay, for example, be the maximum amount of power contained in the firstM coefficients or values in the reordered partition. Another optimalitycriterion may be the mean square error between the reconstructedsequence of channel quality values and the (measured) original sequenceof channel quality values. This criterion would however imply highertransmitter complexity, as the transmitter may need to reconstruct thesequence to determine the mean squared error for choosing the optimum(re)ordering scheme or parameters. This operation of the transmitter mayalso be considered an iteration of testing the resulting compressedinformation against an optimality criterion as described above.

In this exemplary embodiment, the (re)ordering signalling merely needsto indicate which out of the N_(r) defined (re)ordering schemes has beenselected. This may only require ┌ld(N_(rb))┐ bits for the (re)orderingsignal. Another option would be to define the (re)ordering mapping by atleast one reordering parameter and to vary this parameter(s), forexample, within a given range of parameter values, so as to obtain the(re)ordering fulfilling a certain optimality criterion. In thisvariation, only the at least one reordering parameter may be signalled.This may, for example, be realized in a fashion similar to that outlinedbelow for the signalling of the partitioning and coefficients.

It may be noted that the (re)ordering may be applied to the channelquality values before transformation of values to coefficients, or itmay be applied to the channel quality coefficients obtained aftertransformation of the channel quality values. For example, in FIG. 30,the order of functional blocks 2902 and 3001 may be exchanged. Eitherway the optimality criterion is preferably tested after both the(re)ordering and transformation have been applied.

The (re)ordering of the channel quality values may also be employedtogether with the concept of partitioning. In one embodiment of theinvention, the channel quality values may be (re)ordered prior to theirpartitioning. In another embodiment of the invention the values orcoefficients within a partition may be reordered prior to theirtransformation or encoding, respectively. This may be particularlybeneficial if a compression scheme is employed that is most accurate forsmall data indices. A further advantage of reordering the channelquality values in a partition may be that the reordering allowsachieving a more regular distribution of channel quality values in apartition, which in turn yields that most power of the reorderedpartition values may be found in only a very low number of coefficientsof the DCT transform. Hence, according to one embodiment, the reorderingis performed such that the reordered partition has a more regulardistribution of channel quality values than the original partition priorto reordering. The (re)ordering may be, for example, a sorting orshifting of channel quality values in a partition. Those skilled in theart will perceive that the method of (re)ordering may be in some wayknown to the receiver e.g., by signalling or convention.

Generally, the (re)ordering of the data may be signalled to the receiveras well in the channel quality information, unless the (re)orderingalgorithm is known a priori (e.g., using a fixed permutation pattern) toboth the transmitter and the receiver. Allowing for an arbitrary(re)ordering may impose heavy demands on the amount of bits that need tobe signalled to indicate the reordering applied to the data.

Hence, according to one embodiment of the invention one out of a limitednumber N_(r) of (re)ordering mappings (e.g., using interleavers) thatare employed by the transmitter is determined (e.g., in atrial-and-error fashion). For example, the transmitter may obtain datareordered partitions using each of the defined (re)ordering algorithmsprior to transformation, thus obtaining N_(r) reordered partitions. Outof these, the reordered partition may be chosen for transmission (aftercompression of the coefficients/values) that fulfils a certainoptimality criterion. As mentioned above, such an optimality criterioncould be the maximum amount of power contained in the first Mcoefficients or values in the reordered partition. In this exemplaryembodiment, the (re)ordering signalling merely needs to indicate whichout of the N_(r) defined (re)ordering schemes has been selected. Thismay only require ┌ld(N_(rb))┐ bits for the (re)ordering signal.

Another optimality criterion may be the minimal variance or minimum meansquare error when comparing the original channel quality values with thereconstructed channel quality values from the reordered partition. Inthis exemplary embodiment, the (re)ordering signalling merely needs toindicate which out of the N_(r) defined (re)ordering schemes has beenselected. This may only require ┌ld(N_(rb))┐ bits for the (re)orderingsignal.

According to another embodiment of the invention, an interleaver or(re)ordering algorithm is used to generate a number of N_(r) interleavesor (re)ordering realizations by using at least one variable interleaveror (re)ordering parameter. The particular choice which out of the N_(r)interleaver or (re)ordering realizations is employed by the transmitterto transmit the channel quality information is determined e.g., in atrial-and-error fashion according to an optimality criterion as above,mutatis mutandis. In this embodiment, the transmitter merely needs toindicate the at least one employed interleaver or (re)ordering parametervalue for the selected interleaver or (re)ordering mapping indicatingthe permutation/interleaving of the input sequence. Alternatively, thetransmitter merely needs to indicate which out of the N_(r) generatedrealizations has been selected.

The (re)ordering approach may, for example, be particularly advantageousif a “First-M DCT” scheme or similar low-index compression schemes isemployed to encode the channel quality values of a partition.

Partitioning of the Channel Quality Values

In most embodiments having been discussed so far, a partitioningaccording to the channel quality values on a resource unit basis hasbeen used. However other classifications can also be used to create thepartitions. In one embodiment, the partitioning is based upon whatmodulation and coding scheme may be supported by a resource unit at agiven target error rate. In another embodiment, the partitioning isbased on the variation of the channel within a resource unit, such thatresource units with nearly constant channel are grouped in onepartition, and resource units with a fluctuating channel are grouped ina second partition. In another embodiment, a combination ofclassification criteria mentioned is used to create the partitions.

The partitioning may further be determined over each or a combination ofthe following dimensions:

-   -   Time unit (e.g., timeslot, resource block, radio frame,        subframe, transmission time interval, millisecond, etc.)    -   Frequency unit (e.g., transmission bandwidth, carrier bandwidth,        subband, resource block, etc.)    -   Antenna unit (e.g., transmit antenna, receive antenna, antenna        array unit, MIMO channel, etc.)    -   Code unit (e.g., spreading code number or ID)    -   Polarization angle (e.g., horizontal, vertical, circular, etc.)

Partition Affiliation Signalling

To signal the assignment of a respective resource unit to a respectivepartition, i.e., the partition affiliation, the following methods may beused:

-   -   In one example, a map of a size equal to the number of resource        units is transmitted, each map element representing a resource        unit index, where e.g., a first value (e.g., “0”) signifies        assignment to a first partition, and a second bit value (e.g.,        “1”) signifies assignment to a second partition. In case of only        two partitions, the map is preferably constructed as a bitmap.        Otherwise for each map element multiple bits may be required.        The bitmap is exemplified in FIG. 15 as already indicated above.    -   Another exemplary method is the use of a combination index. For        a number of resource units N_(rb), and a number of resource        units assigned to a first partition N₁, there exist only

$\quad\begin{pmatrix}N_{rb} \\N_{1}\end{pmatrix}$

combinations of possible assignments. Therefore it is sufficient tosignal which of these

$\quad\begin{pmatrix}N_{rb} \\N_{1}\end{pmatrix}$

combinations is transmitted. This requires

$\left\lceil {{ld}\begin{pmatrix}N_{rb} \\N_{1}\end{pmatrix}} \right\rceil$

bits. In case of only two partitions, it is sufficient to signal theassignment of resource units to one partition, as the remaining resourceunits automatically belong to the other partition. To reduce thesignalling in this case, it may be advantageous that the signalling isdone for the partition that contains fewer resource units.

Partition Value/Coefficient Signalling

As indicated above, if not using an encoding scheme where the indices ofthe signalled channel quality coefficients or values are known to thereceiver a priori, it may be necessary to signal the indices of thetransmitted coefficients or values. For each partition, the indices ofthe signalled coefficients or values may be signalled in the followingfashions:

-   -   A bitmap of a size equal to the size of the partition may be        transmitted, each bit representing a value/coefficient index,        where a first bit value (e.g., “0”) signifies no transmission of        the respective value/coefficient, and a second bit value (e.g.,        “1”) signifies transmission of the respective value/coefficient.        This method imposes no a priori restriction on the number of        values/coefficients to be transmitted. This solution is        exemplified in FIG. 13, FIG. 18, FIG. 19, FIG. 23, FIG. 25 and        FIG. 27.    -   Combination Index; assuming that the number of transmitted        coefficients M_(p) and the total number of coefficients in a        partition M₀ are known, there exist (basic statistics) only

$\quad\begin{pmatrix}M_{0} \\M_{p}\end{pmatrix}$

combinations of possible coefficient transmissions. Therefore it is Psufficient to signal which of these

$\quad\begin{pmatrix}M_{0} \\M_{p}\end{pmatrix}$

combinations is transmitted. This requires

$\left\lceil {{ld}\begin{pmatrix}M_{0} \\M_{p}\end{pmatrix}} \right\rceil$

bits. This may be done for each partition individually. The approach mayP be applied to transmitted values instead of transmitted coefficientsmutatis mutandis.

-   -   The coefficients are signalled for both partitions jointly;        There can be a bitmap equal to the number M₀ of coefficients for        all partitions, where the first M₁ bits represent the        coefficient indices of the first partition, and the final M₂        bits represent the coefficient indices of the second partition        M₁+M₂=M₀. A first bit value (e.g., “0”) signifies no        transmission of the respective coefficient, and a second bit        value (e.g., “1”) signifies transmission of the respective        coefficient. This approach may be applied to values instead of        coefficients mutatis mutandis.    -   Also for signalling the coefficient indices a combination index        may be used. The coefficients may, for example, be signalled for        both partitions jointly; assuming that the total number of        transmitted coefficients for all partitions together is M_(s)        and the total number of coefficients for all partitions M₀ are        known, there exist only

$\quad\begin{pmatrix}M_{0} \\M_{s}\end{pmatrix}$

index combinations of possible coefficient transmissions. Therefore itis sufficient to signal which of these

$\quad\begin{pmatrix}M_{0} \\M_{s}\end{pmatrix}$

index combinations is transmitted. This requires

$\left\lceil {{ld}\begin{pmatrix}M_{0} \\M_{s}\end{pmatrix}} \right\rceil$

bits. This approach may be applied to values instead of coefficientsmutatis mutandis.

-   -   In all of the above options, any DC component of any partition        may be exempted from signalling if it is always transmitted.        Persistent transmission of the DC component may be advantageous        since this is equivalent to the average power level within a        partition. With the numerology defined above, e.g., instead of

$\left\lceil {{ld}\begin{pmatrix}M_{0} \\M_{p}\end{pmatrix}} \right\rceil,{{only}\mspace{14mu} \left\lceil {{ld}\begin{pmatrix}{M_{0} - 1} \\{M_{p} - 1}\end{pmatrix}} \right\rceil}$

bits are necessary for the coefficient index signalling. Similarly otherindices may be designated a priori for persistent transmission, up tothe extreme that always the identical coefficient indices aretransmitted. Obviously in the latter case there is no need forsignalling the indices for such a partition. Generally this may be doneseparately for each partition, or for the indices of all partitions, sothat there would be no index signalling at all.

Assuming that there are two partitions, and that the signalling for theassignment to partitions (partition affiliation) as well as for thetransmitted coefficient indices uses a combination index, respectively,and furthermore assuming that the DC component for each partition isalways transmitted, we may calculate the number of required bits forsignalling for the proposed scheme as

${{D \cdot \left( {M_{1} + M_{2}} \right)} + \left\lceil {{ld}\begin{pmatrix}N_{rb} \\M_{0}\end{pmatrix}} \right\rceil + \left\lceil {{ld}\begin{pmatrix}{M_{0} - 1} \\{M_{1} - 1}\end{pmatrix}} \right\rceil + \left\lceil {{ld}\begin{pmatrix}{N_{rb} - M_{0} - 1} \\{M_{2} - 1}\end{pmatrix}} \right\rceil},$

where for clarity reasons the partition affiliation andvalue/coefficient index fields are separated. If these are combined intoa single index field, some bit(s) may be saved additionally, as thenumber of required bits may then be calculated as

${D \cdot \left( {M_{1} + M_{2}} \right)} + \left\lceil {{{ld}\begin{pmatrix}N_{rb} \\M_{0}\end{pmatrix}} + {{ld}\begin{pmatrix}{M_{0} - 1} \\{M_{1} - 1}\end{pmatrix}} + {{ld}\begin{pmatrix}{N_{rb} - M_{0} - 1} \\{M_{2} - 1}\end{pmatrix}}} \right\rceil$

Reduced Partition Value/Coefficient Signalling

As identified previously, the signalling of the value/coefficientindices typically makes up a non-negligible part of the requiredsignalling. Therefore it may be advantageous to use only a singlevalue/coefficient index signal field that is valid for more than onepartition.

In the example of FIG. 16 and FIG. 17, it has been determined that forthe first partition, three coefficients should be chosen for compressingthe coefficients of partition T₁, and the same number of coefficientsfor partition T₂. Considering the “strongest” criterion for partitionT₁, coefficients c₁ ¹, c₄ ¹, and c₅ ¹, should be chosen fortransmission, as also shown in FIG. 18. In order to save the signallingfor the coefficients of partition T₂, the coefficients at the sameindices may be chosen for transmission, i.e., coefficients c₁ ², c₄ ²,and c₅ ². Obviously these coefficients may generally not be thestrongest coefficients of partition T₂. In principle the choice of whatcoefficients are transmitted may be based on any partition. In oneembodiment, the coefficients are chosen so as to represent the strongestcoefficients in the partition representing the strongest resource units.In another embodiment, the choice of coefficients is based upon thecoefficient-wise average magnitude of at least two partitions.

In case that there is not an equal number of coefficients for thepartitions, a coefficient for a non-existent index in a partition may beset to a “virtual” zero for the purposes of reduced signalling. Forexample, if coefficient c₁₀ had been chosen for transmission of bothpartitions, the value transmitted for partition T₁ should be zero, asthe transform for partition one contains only 5 coefficients. Likewiseif averaging is used according to one of the mentioned embodiments, acoefficient for a non-existent index in a partition may be set to a“virtual” zero for the purposes of determining the coefficient-wiseaverage magnitude of at least two partitions.

The effect of the reduced coefficient signalling, using the samecoefficients for partition T₂ as for partition T₁, can be seen in FIG.21. FIG. 21 illustrates the channel state as in FIG. 14 and areconstruction of channel quality values from compressed partition-wiseDCT with reduced coefficient signalling overhead according to anexemplary embodiment of the invention. The reconstruction of the channelquality values based on a reduced amount of channel quality informationshows larger deviations from the true channel than the reconstructionincluding the full partition coefficient signalling. However the savingin signalling information may justify this loss.

Table 2 below illustrates the channel quality values of the channel aswell as the reconstructed channel quality values using an encodingscheme as suggested with respect to FIG. 14, FIG. 16 and FIG. 17 as wellas the reconstructed channel quality values using an encoding scheme assuggested with respect to FIG. 14, FIG. 16 and FIG. 17 and in additionreducing the signalling information further, by signalling thecoefficients of partition T₂, the coefficients at the same indices maybe chosen for transmission for partition T₁, i.e., coefficients c₁ ², c₄², and c₅ ² as discussed above. A graph of the numerical values is shownin FIG. 20 and FIG. 21 respectively.

Resource Channel Partition-wise Partition-wise Reconstruction Unit IndexState Reconstruction (reduced signalling) 1 0.69 1.11 0.43 2 0.58 1.120.59 3 1.31 1.15 0.86 4 1.61 1.17 1.14 5 1.15 1.15 1.35 6 0.67 1.09 1.417 1.45 0.97 1.32 8 2.31 2.35 2.35 9 3.12 3.06 3.06 10 2.41 2.30 2.30 110.67 0.81 1.12 12 0.15 0.64 0.89 13 0.47 0.47 0.70 14 0.30 0.36 0.61 150.21 0.32 0.63 16 0.32 0.39 0.74 17 0.71 0.55 0.87 18 2.57 2.57 2.57 192.50 2.64 2.64 20 2.10 0.79 0.99 21 0.93 1.07 1.04 22 0.85 1.34 1.05 231.49 1.56 1.02 24 2.07 1.67 1.00

As can be recognized from the table both compression schemes allow for avery accurate reconstruction of the channel quality values for thestrongest coefficients of the real channel state. The suboptimum choiceof the channel quality coefficients for signalling for the secondpartition in the reduced signalling scheme in the right column is mainlyreflected in the less accurate reconstruction of channel quality valuesof low power (e.g., for indices 11 to 17). However, these low powermeasures are typically less relevant, as same should be not be chosenfor data transmission by the respective transmitter (i.e., should not beassigned to the terminal for transmission).

It should be noted that the reduced signalling approach outlined herefor partition coefficients may be applied to partition values mutatismutandis.

Channel Quality Value

The channel quality value mentioned herein may be each of or acombination of the following parameters, measures, or values:

-   -   Signal-to-Noise ratio (SNR)    -   Signal-to-Interference ratio (SIR)    -   Signal-to-Noise-plus-Interference ratio (SINR)    -   Channel coefficient    -   Channel gain or attenuation    -   Modulation scheme indicator    -   Coding scheme indicator    -   Modulation and coding scheme (“MCS”) indicator

It should be obvious to those skilled in the art that the expressionthat is used widely in the detailed description about “strongestresource units” etc. is referring to a Signal-to-Noise ratio or aSignal-to-Interference ratio or a Signal-to-Noise-plus-Interferenceratio, or generally any measure that relates to a signal strength.However the interpretation for other measure mentioned above can beadapted mutatis mutandis. For example, a strong Signal-to-Interferenceratio may also be expressed as a modulation scheme indicator thatindicates a high-order modulation scheme (e.g., 16-QAM, 64-QAM, etc.),or as a coding scheme indicator that indicates a weak coding scheme(e.g., by a high coding rate), and so forth. Those skilled in the artwill readily be able to derive the corresponding interpretations forother measures or combinations of any measures.

A channel quality value may be determined over each or a combination ofthe following dimensions:

-   -   Time unit (e.g., timeslot, resource block, radio frame,        subframe, transmission time interval, millisecond, etc.)    -   Frequency unit (e.g., transmission bandwidth, carrier bandwidth,        subband, resource block, etc.)    -   Antenna unit (e.g., transmit antenna, receive antenna, antenna        array unit, MIMO channel, etc.)    -   Code unit (e.g., spreading code number or ID)    -   Polarization direction (e.g., horizontal, vertical, circular,        etc.)

The following examples of transmission technologies should provideadditional understanding to those skilled in the art how to beneficiallyemploy the invention.

In an FDM(A) transmission scheme, N_(rb) data resources are available infrequency domain. Therefore also the channel quality measure may beobtained as a frequency-domain variable of N_(rb) values. A firstpartition may consequently contain those frequency resource blocks withthe M₁ strongest channel quality measures, while a second partitioncontains the remaining M₂ channel quality measures. It may be noted thatthis approach may also be used in the special case of OFDM(A), as it canbe seen as a special instance of an FDM(A) transmission.

In a multi-antenna transmission scheme, the channel quality value mayvary from one antenna to the other. Those skilled in the art willrecognize that this is valid both for transmit and receive antennas. Inparticular with respect to MIMO technologies, the communication systemwill generally consist of N_(MIMO) MIMO data streams, for each of whicha plurality of channel quality measures may be obtained if e.g., eachstream uses an FDM transmission scheme. Consequently a first partitionmay contain the channel quality measures valid for a first MIMO datastream, while a second partition may contain the channel qualitymeasures for a second MIMO data stream.

Number of Partitions

Most exemplary embodiments relate to the concept of partition-wisecompression using two distinct partitions. However the conceptspresented can easily be extended into an arbitrary number of partitions.

Hierarchical Partitioning

In another embodiment of the invention not only the original sequence ofchannel quality values may be partitioned, but also the resultingpartitions may be again divided into sub-partitions. Generally, a firstpartitioning is made to create partitions A_(i). In a second timeinstant, the data from at least one of said partitions A_(i) is furtherpartitioned to create partitions B_(i,j). In this way, i denotes theindex of the parent partition, while j denotes the index of the childpartition belonging to parent partition i. Compression may be employedin any of the parent or child partitions according to any of the methodsoutlined in the present invention. This may be used to further increasethe granularity and accuracy of the compression and reconstruction.

It may be noted that such hierarchical partitioning may be beneficiallyemployed in a MIMO case. As mentioned above, a first partition A₁ maycontain the channel quality measures valid for a first MIMO data stream,while a second partition A₂ may contain the channel quality measures fora second MIMO data stream. Then a first sub-partition B_(1,1) maycontain the strongest channel quality measures contained in partitionA₁, while a second sub-partition B_(1,2) may contain the remainingchannel quality measures contained in partition A₁. This can be appliedmutatis mutandis to partition A₂ and sub-partitions B_(2,1) and B_(2,2).

Transmission of Channel Quality Information

In another embodiment of the invention, the encoded and/or compresseddata of all partitions may be transmitted at the same time. However,other solutions may be possible, as outlined in the following.

For example, also a partition-wise successive (serial) transmission ofthe encoded channel quality information is possible. At a first timeinstance, the channel quality information for a first partition istransmitted. At a second time instance, the channel quality informationfor a second partition is transmitted. The order may be predetermined,signalled, or determined according to e.g., a deviation criterion:channel quality information is transmitted for that partition, for whichthere occurs the biggest change compared to the previous transmittedcompressed data for that partition.

Another option is the use of a successive (serial) transmission of theencoded channel quality information components. At a first timeinstance, a first coefficient of the channel quality information istransmitted. At a second time instance, a second coefficient of thechannel quality information is transmitted. This may be employedpartition-wise (i.e., the coefficients for a first partition aretransmitted before the coefficients for a second partition), or in around-robin or similar fashion (i.e., a first coefficient is transmittedfor a first partition, followed by a first coefficient for a secondpartition, followed by a second coefficient for the first partition,etc.).

Another option is the use of a successive (serial) transmission of theencoded channel quality information components. At a first timeinstance, for example, the partition affiliation signal is transmitted,while the value/coefficient signal for the at least one partition istransmitted at an at least second time instance.

A further option is to update channel quality information. According toone embodiment, only the difference of the channel quality informationfor a partition between a first transmission instance and a secondtransmission instance is transmitted. Said difference may either referto the transmitted channel quality information at said firsttransmission instance, or refer to the combination of several previouslycompressed data transmission instances.

Another option to transmit the encoded channel quality informationaccording to a further embodiment of the invention may be apartition-wise update/transmission interval. For a first partition,advantageously one that consists mainly of strong resource units, thechannel quality information is transmitted using a firstupdate/transmission interval. For a second partition, the channelquality information is transmitted using a second update/transmissioninterval. Preferably the first update/transmission interval is shorterthan the second update/transmission interval.

It should be noted that the aforementioned transmission options in timedomain can be easily extended or changed to frequency domain, codedomain, antenna domain, polarization domain, etc. mutatis mutandis.

Further, as already briefly mentioned above it is to be noted that theconcepts of the invention outlined in various exemplary embodimentsherein may be advantageously used in a mobile communication system asdescribed in the Technical Background section that may, for example,have an architecture as exemplified in FIG. 28. The mobile communicationsystem may have a “two node architecture” consisting of at least oneAccess and Core Gateway (ACGW) and Node Bs. The ACGW may handle corenetwork functions, such as routing calls and data connections toexternal networks, and it may also implement some RAN functions. Thus,the ACGW may be considered as to combine functions performed by GGSN andSGSN in today's 3G networks and RAN functions as, for example, radioresource control (RRC), header compression, ciphering/integrityprotection and outer ARQ. The Node Bs may handle functions as, forexample, segmentation/concatenation, scheduling and allocation ofresources, multiplexing and physical layer functions. For exemplarypurposes only, the NodeBs are illustrated to control only one radiocell. Obviously, using beam-forming antennas and/or other techniques theNodeBs may also control several radio cells or logical radio cells.Further, a MIMO transmission scheme may be utilized in the communicationwith the different mobile stations or terminals.

In this exemplary network architecture, a shared data channel may beused for communication on uplink and/or downlink on the air interfacebetween mobile stations (UEs) and base stations (NodeBs). This shareddata channel may have a structure as shown in FIG. 1 and/or may beviewed as a concatenation of subframes as exemplarily illustrated inFIG. 2 or FIG. 3. According to an exemplary embodiment of the invention,the shared data channel may be defined as in the Technical Backgroundsection herein or as in 3GPP TR 25.814, available at http://www.3gpp.organd incorporated herein by reference.

In the embodiments of the invention described herein, the information onthe channel state may be used to communicate a “snapshot” of the channelquality at a given time instance or over a time interval. If informationon the channel state should be used for scheduling or link adaptation, ashort report interval may be advantageous. However, even if the reportinterval of the channel state information is not minimal, the receivercould utilize the information on the channel state in the past for theprediction of a future channel state, which may allow for an adequatescheduling and/or link adaptation.

In some embodiments of the invention, the receiver (e.g., Node B in FIG.28) of the information on the channel state may also comprise ascheduling for scheduling the mobile stations and/or a link adaptationentity for performing link adaptation on the communication channel. Themobile terminals served by a base station (i.e., the receiver in thisexample) may receive information on the channel state from the mobilestations to facilitate scheduling and/or link adaptation.

It should be noted that, particularly in a mobile communication system,the transmitted channel quality information may need to be protectedagainst errors. To this end, one or more of well-known techniques likeerror detection coding (e.g., CRC checksum), forward error correction(Convolutional code, turbo code, Reed-Solomon code), automatic repeatrequests (ARQ), etc. may be employed prior to transmission of theencoded channel quality information. Obviously same techniques should beprocessed appropriately in the receiver after reception prior todecoding of channel quality information.

Moreover, it should be noted that in another embodiment of the inventionany parameter used to control one or more aspects of the partitioning,transformation or encoding may be determined by a network managemententity, e.g., a NodeB. In this case, the respective control parametersmay be signalled from the network to the channel quality informationtransmitter (e.g., a mobile station) using control signalling, e.g.,Layer 1/Layer 2 (L1/L2) control signals on a L1/L2 control channel,control information in a MAC header, or using RRC signalling. Thefrequency of such L1/L2 control signalling for CQI parameters may beperiodic or event-driven. The frequency of the control signalling may bedetermined by a management entity. It may be additionally advantageousto convey different control parameters using control signalling indifferent resources, e.g., using resources that differ in at least oneof:

-   -   Time unit (e.g., different timeslot, resource block, radio        frame, subframe, transmission time interval, millisecond, etc.)    -   Frequency unit (e.g., different carrier frequency, subband,        resource block, etc.)    -   Antenna unit (e.g., different transmit antenna, receive antenna,        antenna array unit, MIMO channel, etc.)    -   Code unit (e.g., different spreading code number or ID)    -   Polarization direction (e.g., horizontal, vertical, circular,        etc.)

Any event mentioned previously or hereafter that may cause thetransmitter to decide to change one or more channel quality informationparameters (e.g., number of partitions, number of values/coefficientsper partition, transformation parameters, number of transmittedvalues/coefficients per partition, number of available/required bits forchannel quality information, etc.) may as well or instead cause themanagement entity to decide a change of parameter(s) mutatis mutandis.In case there is a change to the parameters, same may be conveyed to thechannel quality information transmitter using e.g., a control signal, asoutlined in the previous paragraph.

Generally, it may be also assumed that the scheduling and linkadaptation are performed on resource unit basis. For example, thesmallest unit of (radio) resources (also referred to as a resource blockor resource unit) that can be allocated in an OFDMA system is typicallydefined by one subframe in time domain and by one subcarrier/subband inthe frequency domain. Similarly, in a CDMA system this smallest unit ofradio resources is defined by a subframe in the time domain and a codein the code domain. Generally, a resource unit (for scheduling may) bedefined as a unit formed by a combination of at least two out of asubframe in the time domain, a subcarrier/subband in the frequencydomain, a code in the code domain and antenna in MIMO.

It should be noted that the channel state/quality is reported for a setof resource units into which the channel may be divided. These resourceunits may or may not be similar to the resource units based on which themobile stations are scheduled and/or based on which link adaptation maybe performed. For example, assuming an OFDM shared channel, the resourceunits for which the channel state is reported may either correspond tothe resource blocks based on which scheduling and/or link adaptation isperformed. Alternatively, the transmitting entity (mobile stations)providing the channel state information may also report the channelstate on a resource unit-basis where the resource unit is equivalent toone or more subframes in the time domain and one or moresubcarrier/subband in the frequency domain. This principle may also beextended to the code domain. In other words, it is not prerequisite thatthe granularity of the channel state report is identical to thegranularity in which resource may be scheduled in the system and/or linkadaptation is performed.

For communication in the mobile communication system e.g., an OFDMscheme, a MC-CDMA scheme or an OFDM scheme with pulse shaping(OFDM/OQAM) may be used. In some embodiments the scheduler may schedulethe resources on a per-resource block basis (i.e., per subframe basis inthe time domain) or on a transmission time interval (TTI) basis, whereinin the latter case it may be assumed that a TTI comprises one or moresubframes in the time domain.

In one embodiment of the invention, channel quality information isreported for a channel having 10 MHz bandwidth and consisting out of 600subcarriers with a subcarrier spacing of 15 kHz. The 600 subcarriers maythen be grouped into 24 subbands (each containing 25 subcarriers), eachsubband occupying a bandwidth of 375 kHz. Assuming that a subframe has aduration of 0.5 ms, a resource block (RB) spans over 375 kHz and 0.5 ms.

Alternatively, a subband may consist of 12 subcarriers, 50 of thosesubbands constituting the available 600 subcarriers. With a transmissiontime interval (TTI) of 1.0 ms, equivalent to 2 subframes, a resourceblock (RB) spans over 300 kHz and 1.0 ms in this example.

Another embodiment of the invention relates to the implementation of theabove described various embodiments using hardware and software. It isrecognized that the various embodiments of the invention may beimplemented or performed using computing devices (processors). Acomputing device or processor may, for example, be general purposeprocessors, digital signal processors (DSP), application specificintegrated circuits (ASIC), field programmable gate arrays (FPGA) orother programmable logic devices, etc. The various embodiments of theinvention may also be performed or embodied by a combination of thesedevices.

Further, the various embodiments of the invention may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example, RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

In the previous paragraphs various embodiments of the invention andvariations thereof have been described. It would be appreciated by aperson skilled in the art that numerous variations and/or modificationsmay be made to the present invention as shown in the specificembodiments without departing from the spirit or scope of the inventionas broadly described.

It should be further noted that most of the embodiments have beenoutlined in relation to a 3GPP-based communication system and theterminology used in the previous sections mainly relates to the 3GPPterminology. However, the terminology and the description of the variousembodiments with respect to 3GPP-based architectures is not intended tolimit the principles and ideas of the inventions to such systems.

Also the detailed explanations given in the Technical Background sectionabove are intended to better understand the mostly 3GPP specificexemplary embodiments described herein and should not be understood aslimiting the invention to the described specific implementations ofprocesses and functions in the mobile communication network.Nevertheless, the improvements proposed herein may be readily applied inthe architectures described in the Technical Background section.Furthermore the concept of the invention may be also readily used in theLTE RAN currently discussed by the 3GPP.

1. An apparatus for reporting channel quality information in acommunication system, the apparatus comprising: one or more processorsto: partition channel quality values, based on a channel qualityinformation reporting parameter, into at least two partitionscorresponding to different frequency bands in a bandwidth associatedwith the communications system, and encode a channel quality value ofthe channel quality values of at least one of the at least twopartitions to obtain signaling information on channel quality, includingat least one of first channel quality information and second channelquality information, based on the channel quality information reportingparameter, wherein the second channel quality information is differentfrom the first channel quality information; and a transmitter totransmit the signaling information on the channel quality by reportingthe first channel quality information or the second channel qualityinformation at different reporting frequencies depending on the channelquality information reporting parameter.
 2. The apparatus according toclaim 1, wherein the first channel quality information corresponds to afirst group of resource blocks and the second channel qualityinformation corresponds to a second group of resource blocks.
 3. Theapparatus according to claim 2, wherein the first group of resourceblocks is larger than the second group of resource blocks.
 4. Theapparatus according to claim 3, wherein the first channel qualityinformation includes an average of channel quality values.
 5. Theapparatus according to claim 1, wherein the first channel qualityinformation is sent less frequently than the second channel qualityinformation.
 6. The apparatus according to claim 1, wherein there is achannel quality value for each resource unit of a channel.
 7. A methodfor reporting channel quality information in a communication systemcomprising the following steps performed by a transmitter: partitioningchannel quality values, based on a channel quality information reportingparameter, into at least two partitions corresponding to differentfrequency bands in a bandwidth associated with the communicationssystem; encoding a channel quality value of the channel quality valuesof at least one of the at least two partitions to obtain signalinginformation on channel quality, including at least one of first channelquality information and second channel quality information, based on thechannel quality information reporting parameter, wherein the secondchannel quality information is different from the first channel qualityinformation; and transmitting the signaling information on the channelquality by reporting the first channel quality information or the secondchannel quality information at different reporting frequencies dependingon the channel quality information reporting parameter.
 8. The methodaccording to claim 7, wherein the first channel quality informationcorresponds to a first group of resource blocks and the second channelquality information corresponds to a second group of resource blocks. 9.The method according to claim 8, wherein the first group of resourceblocks is larger than the second group of resource blocks.
 10. Themethod according to claim 9, wherein the first channel qualityinformation includes an average of channel quality values.
 11. Themethod according to claim 7, wherein the first channel qualityinformation is sent less frequently than the second channel qualityinformation.
 12. The method according to claim 7, wherein there is achannel quality value for each resource unit of a channel.
 13. Acomputer-readable medium storing instructions that, when executed by aprocessor of a transmitter, cause the transmitter to report channelquality information in a communication system, by: partitioning channelquality values, based on a channel quality information reportingparameter, into at least two partitions corresponding to differentfrequency bands in a bandwidth associated with the communicationssystem; encoding a channel quality value of the channel quality valuesof at least one of the at least two partitions to obtain signalinginformation on channel quality, including at least one of first channelquality information and second channel quality information, based on thechannel quality information reporting parameter, wherein the secondchannel quality information is different from the first channel qualityinformation; and transmitting the signaling information on the channelquality by reporting the first channel quality information or the secondchannel quality information at different reporting frequencies dependingon the channel quality information reporting parameter.
 14. An apparatusfor receiving channel quality information in a communication system, theapparatus comprising: a receiver to receive signaling information onchannel quality including first channel quality information and secondchannel quality information reported at different reporting frequenciesdepending on a channel quality information reporting parameter, and oneor more processors to decode the signaling information on the channelquality based on the channel quality information reporting parameter toobtain a channel quality value of channel quality values of at least oneof at least two partitions, wherein the channel quality values arepartitioned based on the channel quality information reporting parameterinto the at least two partitions corresponding to different frequencybands in a bandwidth associated with the communications system.
 15. Theapparatus according to claim 14, wherein the receiver is configured toreceive channel quality values from a plurality of transmitters, andwherein the receiving circuitry includes a scheduler to schedule arespective one of the plurality of transmitters taking into account atleast the channel quality value signaled by the respective transmitter.16. The apparatus according to claim 14, wherein the receiver isconfigured to receive channel quality values from a plurality oftransmitters, and wherein the one or more processors are configured toselect at least one link adaptation parameter for link adaptation for arespective one of the plurality of transmitters taking into account atleast the channel quality value signaled by the respective transmitter.17. The apparatus according to claim 16, wherein the at least one linkadaptation parameter is related to at least one of a modulation andcoding scheme, a configuration of a hybrid automatic repeat requestprocess, and transmission power control.